At a vineyard high above the river, we are clinging to a cable as precipitous as the north face of the Eiger. From here, the river barges, as long as football pitches, resemble children's toys. The laughter tumbling through the vines is Thomas Franzen's family picking the harvest's first grapes.

The vineyards on the Calmont cliff have required a head for heights since Roman days. Above the Mosel's most famous convolution, the winemakers of Bremm have created a klettersteig, or climbing path, for bold oenophiles, linking age-old cultivation tracks with ladders and cables. The part Thomas's children are making look like child's play is called Todesangst Ecke or "Scared-to-Death Corner".

This is our third day on the Moselhöhenweg, or Mosel Heights Trail, a long-distance track between Koblenz and Trier, often high above the river, often ambling beside it, via forests and vineyards and picture-book villages. Sixty miles for flying crows, but the moseying Mosel meanders twice as far. Too steep for machines, thousands of vineyards triumph over gravity.

Around AD370 poet Decimus Ausonius penned 480 rhapsodic verses extolling the Romans' beloved Mosella: "Bigger than the Nile, cooler than the Don, nobler than the Tiber…" And after miles of grapes and sunshine, the river coiling around us like a wine-sozzled snake, we begin to get his drift.

On a misty Mosel morning we set out from sleepy Moselkern, up the wooded valley that hides the Mosel's bashful megastar, Burg Eltz. Castles wallpaper the Mosel almost as densely as vines but few medieval strongholds have lasted as well as this one. Yet lit by sunbeams, it looks as make believe as Disneyland. The present owner-occupier, Karl Graf von und zu Eltz, is the 33rd count since his forefathers built it in1157. Every stone remains original.

In the dungeon strong rooms we gape at one of the world's biggest private treasure hoards. It glitters with gold beyond old nobility's most avaricious dreams, making the count's €8 ticket seem paltry by comparison – but then visitors can only reach his castle on foot.

The Mosel Heights Trail was one of Europe's earliest long-distance paths. Roughly tracing the river, it leapfrogs over hills to dodge the meanders. Crossing grassy uplands, it strays in lonely valleys but we follow the "M" signs which magically materialise whenever we get lost and always bring us back to the Mosel in the end.

On maps the trail looks like a trunk road but countless intersecting paths make it possible to weave a personalised itinerary – long or short stages, easy or hard – all the way to Trier; or to make one village a base and explore the well-signed local paths. Today we detour and catch a ferry to Klotten's famous vineyards.

Meanwhile our scenic "M" path to Cochem slogs over the ridge. From the Pinneberg precipice, the mid-Mosel capital looks like an antique map. White ships fringe the quaysides; towers and steeples hug the old bridge. There are cafés, bars and weinstuben, but first we must get down. Our contempt for the chairlift (this is a celebrated vista) evaporates as we gingerly attempt the alarming M-marked track.

Though at heart it remains a 2,000-year-old wine town, Cochem's riverside promenades, castles and squares attract visitors by road, rail and boat. Every weinstube is packed. We spot a booth selling federweisser (the still-fermenting new wine) of which our daily intake increases with the miles.

We devour our evening schnitzel at the historic Alte Thorschenke, Germany's oldest inn, frying since 1332, and where guests can try the four-poster where Napoleon slept in 1804. Mosel cuisine eschews firmly the nouvelle but for schnitzel creativity – multifarious varieties filling every menu – it surely has no peer. To the refined Thorschenke's version we drink a classy Spätburgunder (Teutonic Pinot Noir) from the baron's own vines.

The next morning we are greeted by rain but we pop out above the castle into dazzling sun. The valley looks like a ditch filled with candyfloss and topped with whipped cream.

The gorge's microclimate is Mediterranean; in summer lizards bask in temperatures in the upper nineties (upper thirties Celsius). Wild peaches and figs are distilled into liqueurs. There are apples, plums and walnuts to guzzle as we walk. And grapes everywhere.

Did you know?

The Mosel is 338 miles in length and begins in the Vosges mountains in France

We saunter into Alf at sunset. Linked by ferry to Bullay, the two spic and span villages beam at each other like identical twins. Börmers weinstube looks too old world to be true but Frau Matilde Kaspari, in her nineties, has been the all-in-one bar staff, waitress and proprietress for more than 50 years. Börmers, natürlich, is centuries older.

Jolly senior citizens are sipping wine at tables their great grandparents used. A village adage has it that long-lived winegrowers outnumber long-lived doctors. Frau Matilde seems the proof. She sells only three wines – dry, medium, and sweet – all from Alf vineyards. It is a mere €2 (£1.75) per copious glass, but old-age winemakers drink only good stuff. In the spirit of gemütlichkeit, it seems polite to try all three.

The days blend slowly into one. Early mists melt to sunshine and baking afternoons. On the Saturday, we hear the distant oompah of brass bands from harvest celebrations but the partying in Lieser is its annual fried-fish feast. There is dancing in the square where we scoff our sizzling trout.

We retreat to the river with a bottle of chilled sekt and watch the boats which link the Mosel villages via Bernkastel-Kues, the town no one wants to miss.

In the hard-working wine villages, tourism is secondary, but many growers let guestrooms. We overnight in Klüsserath at Günter Bechtel's winery. The harvest in full swing, clattering carts of grapes scent the village air. The family toils until dusk yet somehow manages to serve a memorable meal. Mother at the stove, sons serve and wash up, father pours their best wines which he sells at takeaway prices.

After our winzerschnitzel, wine-grower schnitzels (deliciously topped with ham, eggs and grapes), which demand harvesters' appetites, Günter offers us a rare 2004 eiswein. It is pressed, he explains, from frozen grapes, and only their quintessence enters the wine.

Two days later we walk into Trier, one-time Roman capital. It must have been the Roman squaddies' favourite posting as each received two litres of Mosel wine a day.

Germany's oldest city merits days to savour, but next morning we must head towards our half-forgotten car. At a sundeck table, feet upon our packs, wineglasses in hands, we glide every inch by boat.

Getting there

Lufthansa (0871 945 9747; www.lufthansa.com) flies daily from London, Birmingham and Manchester to Frankfurt and Düsseldorf from £88 return, with good onward train connections to Koblenz and Trier and all stops in between. Ryanair (0871 246 0000; www.ryanair.com) has three daily flights from Stansted to Hahn (billed imaginatively as Frankfurt).

Driving makes an attractive alternative. P & O (08716 642121; www.poferries.com) has return crossings from Hull to Zeebrugge: one car and two adults cost from £308. One of the perks is filling your boot with some of the great wines you cannot buy here.

River cruising

Several companies include Mosel cruises in their programmes. Viking River Cruises (020 8780 7989; www.vikingrivercruises.co.uk) has departures on October 10, 17, 24 and November 7 on its eight-day 'Castles & Wine’ tour from Nuremberg to Trier, with availability in Category B cabins from £1,945, including full board, flight and six guided tours. Two days are spent on the Mosel, as well the Rhine and Main. Avalon Cruises (0800 668 1836; www.avaloncruises.co.uk), Page & Moy (0844 567 6633; www.pageandmoy.co.uk) and Phoenix Holidays (08444 129900; www.phoenixholidays.co.uk) also offer Mosel cruises.

The inside track

The river roughly divides into three sections served by several companies. Examples of trips include Trier to Bernkastel; Bernkastel to Traben; Traben to Cochem; Cochem to Koblenz; prices range from £8 one-way.

Sailing the whole river from Trier to Koblenz needs at least two overnight stays en route.

Return ticket prices are much better value if you prefer to explore the river in short stretches. Timetable and information in English at www.moselfahrplan.de.

Despite the throngs, bewitching Bernkastel is full of intriguing historic nooks and crannies – the famous Doktor Fountain is an amazing paean in stone to the salubriousness of wine.

When to go

Even when they’re harvesting the Eiswein in winter the Mosel can be lovely, but the passenger-boat season is May 1-October 31, which matches the best walking months. Every time has it glories but high-season is the wine harvest, which starts at the September and runs into November. The Mosel autumns are renowned for Indian summers. We had sunshine every day but pack a waterproof because they say it sometimes rains.

The inside track

The river divides into sections, served by several companies – Traben to Cochem; Trier to Bernkastel; Bernkastel to Traben; Cochem to Koblenz; with prices from £8 one way.

Sailing the river from Trier to Koblenz needs at least two overnight stays en route.

Return ticket prices are much better value if you explore the river in short stretches. Timetable and information in English at www.moselfahrplan.de.